1. Field of the Invention
This invention relates to directional drilling of boreholes in the earth. It relates especially to a downhole drilling tool whcih can be manipulated from the surface to drill either in a vertical or straight position, or in a directional drilling position.
2. Setting of the Invention
Oil and gas are produced from underground formations through wellbores drilled from the surface to the formation. Originally, it was desired to drill the well in as nearly a vertical direction as possible. However, in some cases, due to the particular geometry of the underground formation, it is nearly impossible to drill vertical wells. This is particularly true in steeply dipping formations in which the well keeps wanting to veer off to the updip side. Means is then required to cause the well to drill in the opposite direction. These tools which have been used for this purpose are ordinarily called directional drilling tools. Recently, it has become increasingly popular to drill wells in oriented directions. This is particularly true of offshore production. In those areas, a platform may be erected in water 100 to 200 feet or more deep and many wells drilled from a single platform. The wells will not be drilled in a vertical position, but will be drilled in a slanting or directional position in order to reach a particular subsurface location in the producing formation, which may be one or two miles in a lateral direction from the location of the platform.
Oriented directional drilling is generally at present accomplished by (1) a downhole motor to drive the bit, and a bent sub above the motor that permits orientation and causes the bit to drill in the oriented azimuth; (2) a downhole whipstock which cants the drill pipe in the oriented position; or (3) an arrangement of stabilizers on the lower drill string member which acts with the weight of the drill string members and applied drilling weight to cant the drill string toward either the high or low side of the hole. These methods require a special trip with the drill string to install the appropriate downhole equipment followed by one or more trips after directional drilling to return the bottom-hole drilling apparatus to that required for forward drilling of a full-size hole. Drilling progress may also be slowed during these operations because less than optimum drilling weight and rotary speed can be applied. The efficiency of the operation may be further affected by changes in the oriented direction during drilling due to the reaction between the rotating member and the wall of the hole.
As mentioned above, there are numerous directional drilling tools. The inventor knows of no drilling tool like the one he is claiming here. However, there are directional drilling tools which use the principle of eccentric sleeves. Typical of those are U.S. Pat. Nos. 2,712,434 and 2,173,309.